There are four main types of thyroid cancer papillary, follicular, medullary, and anaplastic. Papillary carcinoma (PC) is the most common type of thyroid cancer, representing up to 80% of all malignant thyroid tumors (Hundahl et al., 1998).
Exposure to radiation to the head and neck during infancy or childhood is correlated with an increased risk of thyroid cancer. The cancer may occur as early as 5 years after exposure or may occur 20 or more years later. Goiter or a family history of thyroid disease is also correlated with an increased risk of developing thyroid cancer.
Prognosis depends on the type of thyroid cancer, whether it is in the thyroid only or has spread to other parts of the body (stage), and the patient's age and overall health. The prognosis is better for patients younger than 40 years who have cancer that has not spread beyond the thyroid.
The majority of PCs are not life threatening and are effectively treated with thyroidectomy followed by radioactive iodine ablation (DeGroot et al., 1990). However, a minority of PCs recur and cause significant morbidity (Hundahl et al., 1998; LiVolsi, 1996). Furthermore, an even smaller minority of PCs undergo progression from well-differentiated carcinoma to either poorly- or undifferentiated carcinoma, an event associated with marked reduction in survival (Giuffrida & Gharib, 2000). What are needed are improved methods for the early diagnosis and treatment of thyroid cancer.